This invention relates to the purification of organohalosilanes. More specifically, this invention relates to a means for chemically converting olefin impurities in organohalosilanes and isolating and recovering the purified organohalosilane.
High-purity organohalosilanes are needed for the ever-increasing quality needs of the industrial manufacture of other organosilanes and organopolysiloxanes. In the preparation of organohalosilanes via the direct reaction of an organic halide with silicon, the crude organohalosilane mixture contains minor amounts of the whole spectrum of hydrocarbon impurities. The olefinic components in many cases cause a separation problem with the commonly used practice of isolating by distillation the desired organohalosilanes contained in the crude reaction product of the direct reaction, the olefin components having boiling points very close to the various organohalosilanes. As impurities in the isolated organohalosilanes, these olefinic materials pose serious quality problems.
Olefins are known to cause color problems in the preparation of organosilane and polyorganosiloxane intermediates and products. In the processing environment to which the direct process crude is exposed, the olefinic materials are easily converted to chlorocarbons by reaction with hydrogen chloride. Chlorocarbons create a problem due to their thermal instability, potentially decomposing into an olefin and hydrogen chloride. As an example, an organohalosilane containing low levels of a chlorocarbon can be converted to a polyorganosiloxane via hydrolysis with the chlorocarbon surviving early process steps, only to dehydrohalogenate causing an acidity problem with the hydrolyzate product and also color problems due to the olefin formed.
Motomiya, Japanese Patent Publication No. 50-39649, published Dec. 18, 1975, discloses a method for purification of organohalosilanes in which a Lewis acid or a metal hydroxide is used to convert unsaturated and saturated hydrocarbon impurities to polymers, facilitating recovery of purified organohalosilanes. Motomiya demonstrates that the presence of a hydrogen-containing silane compound is not necessary for the conversion of the hydrocarbons to a polymer to proceed. No mention is made of the reaction of an olefinic material with a hydrogen-containing silicon compound in which there is at least one hydrogen atom attached to a silicon atom in the presence of a Group VIII metal catalyst to form a higher-boiling organohalosilane to facilitate isolation and separation of the desired organohalosilane with enhanced purity.
Clay et al., Japanese Patent Publication No. 59-137312, published Aug. 7, 1984, discloses a method for purification of chlorosilanes in which chlorohydrides of elements from Group III or IV of the Periodic Table are contacted with chlorine to convert these chlorohydrides to chlorides to facilitate separation of these impurities from the desired chlorosilanes via distillation. No mention is made of applying this method to the removal of olefinic materials from organohalosilanes.